In a plasma chemical vapor deposition (CVD) process, a film is formed over a wafer by transforming a material gas, which is fed to a reaction chamber, into plasma through application of a high-frequency electric power. After the film formation is completed, feeding of the material gas is first suspended, and application of the high-frequency electric power is then suspended. This is intended to hinder generation of particles.
However, particles are generated because the material gas remaining in the reaction chamber brings about an abnormal reaction during a period of time from suspension of feeding of the material gas to suspension of application of the high-frequency electric power. The generated particles drop to the superficial surface of the wafer and contaminate the wafer. Since there is a fear that the particles may deteriorate the properties of devices, the particles have to be removed from the wafer.
As a method of removing particles from a wafer, lift-off based on wet etching or polishing based on chemical mechanical polishing (CMP) is generally adopted.
However, if particles having dropped to the superficial surface of a wafer adhere to the wafer, it is hard to remove the particles through wet etching. In the CMP process, even a formed film may be peeled off while the particles are being removed.